The present invention relates to processing equipment for utilization in reactors for treatment of wastewater with microorganisms to remove impurities and, in particular, to sequencing batch reactors.
In the early history of wastewater treatment by microorganisms, the wastewater was often batched and treated by various processes of agitation, aeration or the like. With the amount of wastewater to be treated increasing in volume and in impurities, batch treatment became fairly labor intensive and was eventually substantially replaced by continuous wastewater treatment processes in the 1920's and 1930's.
However, with the relatively recent innovation of computers which can be programmed to control valves, motors, etc. in the wastewater treatment process system, batch reactors again appear to be a viable alternative and offer attractive advantages over continuous processes.
In particular, batch reactors have certain control and economic advantages over continuous reactors, especially where the control can be accomplished by as many or fewer manhours as are required to run like quantity and quality continuous reactors. Sequencing batch reactors which retain a certain amount of sludge within the reactor, fill, aerate and/or agitate, settle, decant, and remove excess sludge, have been shown to be highly effective in treatment of wastewater. As is described in greater detail below, sequencing and timing of the various steps in the wastewater treatment can be varied somewhat to take advantage of particular conditions to achieve different treatment objectives such as treatment of different types of pollutants and the ability to process even with relatively variable flow patterns without substantial loss of effluent quality.
A reactor utilizing jet aerators provides advantages, since this type of aerator may be utilized to agitate and/or aerate without substantial modification to the apparatus. However, the relativley small nozzles of jet aerators have, in the past, presented problems in the industry, since they are highly susceptiple to blockage by debris in the wastewater. Some previous attempts to utilize jets have developed systems that require removing the equipment with jets attached from the reactor so the jets can be cleaned which is very labor intensive and time consuming. Other users of jet nozzles have utilized cleaning methods which created a relatively very weak cleaning effect at the nozzle at low flow rates utilizing air lift principles.
As noted above, for sequencing batch reactors to be most economic, it is important to reduce the manhours necessary to operate the reactor. This may be accomplished by automating as much of the process as possible, in particular, substantially or completely controlling the process by means of a programmable computer or the like. In such a controlled process, it is also important to efficiently handle a wide range of flow rates into the process without significant degradation in the quality of the effluent. In such a controlled process, it is further important to minimize energy requirements and sludge production.
In wastewater treatment reactors, it is also desirable to reduce the number of pumps in order to keep capital costs at a minimum, to reduce the chance of failure of equipment, reduce maintenance requirements and to simplify the process in general. However, it is necessary to allow fresh wastewater to be treated to flow into the reactor, to withdraw excess sludge from the reactor, to circulate fluid within the reactor through an agitation/aeration system and to be able to backflush through the agitator/aeration system to clean nozzles associated therewith so as to restore full operation thereof when the nozzles become plugged with debris suspended in the wastewater. In addition, the treated wastewater and excess residual sludge must be removed from the reactor.
Each of the fluid handling steps noted above, including nozzle cleanout, potentially requires a pumping mechanism or must rely on another fluid driving force such as gravity to accomplish the desired goal. For the reasons discussed above, it is desirable that the system be designed such that all of these steps be accomplished by as few pumping mechanisms as possible, preferably a single unit.
During some alternative treatment processes utilized in sequencing batch reactors for treating specific problem pollutants or during periods of high influent flow rates, such as during heavy rainfalls, it may be desirable to inject wastewater into the reactor during a settling or a decanting operation, so that decanting and filling steps can occur simultaneously.
Previously batch reactors have often been essentially long narrow tanks with baffles to allow influent velocity dissipation at the baffled end, and effluent decanting at the opposite end. Long narrow, baffled tanks involve higher capital costs, require more land area, and generally impose an undesirable constriction on design options. A fixed baffle is sometimes used in such installations to disipate influent velocities, but such a baffle reduces flexibility in control over the conditions which alow microorganism selection. Selective microorganism production helps ensure successful operation and is one of the batch reactors primary advantages.
In order that the incoming influent not disrupt the treated effluent in a reactor vessel of any geometry, the influent should preferably be distributed at multiple locations across the bottom of the reactor to dissipate flow velocity of influent as much as possible and to reduce agitation. Likewise, it is important that sludge be removed in a similar manner so that the heaviest concentrations of sludge at the bottom of the reactor are removed first and preferably so the fluid to be removed does not draw from the upper portions of the reactor, but rather from those lower areas having a high concentration of sludge. High sludge concentrations reduce sludge treatment costs. In many prior art systems, sludge is withdrawn by point type takeoff devices, such that the sludge often becomes diluted by upper layers of fluid entrained with the takeoff fluid due to flow velocity and lack of multiple spaced withdrawl points, with the result that the sludge is relatively less dense in solids and costs more to process in such systems.
In reactors of this type, it is also important that the decanted fluid be able to be removed with as little contamination from the sludge as possible. Therefore, it is desirable that the influent distributing manifold be relatively close to the bottom of the reactor to dissipate velocity of influent, so that influent can, under certain conditions, be added to the reactor as decanted fluid is removed without agitation or contaminating the decanted fluid. It is also desirable that the decanting system draw from near the top of the reactor, slightly beneath the upper layer of fluid so that floating debris is not withdrawn with the decanted fluid. Preferably, the decanting withdrawl system will draw from a relatively fixed distance beneath the upper surface of the reactor throughout the decanting cycle.